A jury has started weighing the case of a Marblehead man charged with killing his pregnant girlfriend and her nearly full-term fetus more than three years ago.

Peter Ronchi faces two counts of first-degree murder in connection with the May 2009 slaying of 42-year-old Yuliya Galperina and the unborn fetus.

The jury started deliberating Tuesday following closing statements by attorneys.

Ronchi 's lawyer is not disputing that his client killed Galperina, but says he suffered from mental illness, was under stress, and did not plan to kill her, doing so in the "heat of passion." The defense says his client is guilty of manslaughter at worst.

Prosecutors counter that Ronchi brought a knife with him to the apartment, changed his clothes after the killing, then fled to Connecticut.